Secondary battery and a method for fabricating the same

Abstract

The adhesion between metal foil serving as a current collector and a negative electrode active material is increased to enable long-term reliability. An electrode active material layer (including a negative electrode active material or a positive electrode active material) is formed over a base, a metal film is formed over the electrode active material layer by sputtering, and then the base and the electrode active material layer are separated at the interface therebetween; thus, an electrode is formed. The electrode active material particles in contact with the metal film are bonded by being covered with the metal film formed by the sputtering. The electrode active material is used for at least one of a pair of electrodes (a negative electrode or a positive electrode) in a lithium-ion secondary battery.

What is claimed is: 
     
       1. An electrode comprising:
 a current collector; 
 a metal film over the current collector, the metal film comprising one of titanium and nickel; 
 an adhesive partly existing between the current collector and the metal film; and 
 an active material layer over the metal film, the active material layer comprising a first graphite particle, a second graphite particle and a third graphite particle, 
 wherein the adhesive comprises an insulating resin, 
 wherein the first graphite particle is covered with a first silicon oxide film, 
 wherein the second graphite particle is covered with a second silicon oxide film, 
 wherein the third graphite particle is covered with a third silicon oxide film, 
 wherein the first graphite particle positions over a gap between the second graphite particle and the third graphite particle, and 
 wherein the metal film penetrates into the active material layer to attach to the first silicon oxide film. 
 
     
     
       2. The electrode according to  claim 1 , wherein the metal film comprises titanium. 
     
     
       3. The electrode according to  claim 1 , wherein the first silicon oxide film forms a silicide with the metal film. 
     
     
       4. The electrode according to  claim 1 , wherein each of the second silicon oxide film and the third silicon oxide film is in contact with the metal film. 
     
     
       5. The electrode according to  claim 1 , wherein the metal film has different thicknesses over the active material layer. 
     
     
       6. The electrode according to  claim 1 , wherein an average thickness of the metal film is 1 μm or more. 
     
     
       7. The electrode according to  claim 1 , wherein the current collector has a thickness of greater than or equal to 10 μm and less than or equal to 30 μm. 
     
     
       8. A secondary battery comprising:
 the electrode according to  claim 1 ; and 
 a counter electrode, 
 wherein a potential of the counter electrode is higher than a potential of the electrode. 
 
     
     
       9. The secondary battery according to  claim 8 , further comprising an electrolyte comprising a solvent. 
     
     
       10. The secondary battery according to  claim 8 , further comprising a solid electrolyte. 
     
     
       11. An electronic device comprising the secondary battery according to  claim 8 .